Method and apparatus for securing software distributed over a network

ABSTRACT

A method and computer executable program code are disclosed to verify the source of software downloaded from a remote site to a client computer over a computer network before the software can be executed on the client computer.

RELATED APPLICATION

The present application claims the benefit of priority from and is acontinuation-in-part of the commonly-owned application Ser. No.09/208,735, filed Dec. 8, 1998, now issued as U.S. Pat. No.: 6,266,774.

FIELD OF THE INVENTION

This invention relates in general to computer networks. In particular,the invention relates to secure ways of distributing software by servercomputers to client computers over a computer network.

BACKGROUND OF THE INVENTION

The public data networks, collectively called the Internet andcolloquially referred to as the Web, are becoming increasingly popular.Among other things, the Internet provides a communication medium todistribute software products to computers that are located at distantplaces. The numerous methods by which sellers of computer softwareprograms deliver executable programs automatically to client computersowned or operated by users are described in the parent application, thedisclosure of which is hereby incorporated by reference.

To understand the invention, it is helpful to understand thedistinctions among the terms content, browser, type-setting program,embedded object and script. These five types of entities are describedbelow in the context of Internet-related software.

Content is the subject matter contained in a web page. Content isdistinguished from the other entities described herein in that contentis not a program; it is the data that is presented to a user.

A web browser, or simply, a browser, is a computer program that providesaccess to the vast resources of the Internet. Typically, this is done byproviding a “window” to the data located on other computers connected tothe Internet. A frame is a part or section of a browser window thatcontains a distinct display area. If a web page is defined to containmultiple frames, each frame can act as an independent display area, andcan download web pages located at different web sites, while displayingthem together in one window on a browser. Alternatively, a web page maycause multiple browser windows to be created on the user's computer. Abrowser can also be described as a “container” of the various componentsit displays. Thus, while the components are embedded in a browser, thebrowser envelops the components.

In general, in a window-based computer system, such as the Windows™ 98™program marketed by the Microsoft Corporation, windows are arrangedhierarchically. A browser program that executes on a window-basedcomputer system is also arranged hierarchically. When a browserapplication is launched on a windows-based computer system, the firstwindow that appears is called “parent window” or “main window” or“top-level” window. This top-level window can later “spawn” or “fork”other windows, which are called “sub-windows” that run otherapplications. A sub-window may be created by executing a script within abrowser window, and may be programmed to run another instance of abrowser program. In such cases, the sub-window is called an “opener”window. Thus, it may be the case that a first window running a browserprogram—a top-level window—is programmed to point to a web site, and asub-window created from the same browser program is programmed to pointto a different web site.

A type-setting program is a presentation program, typically written inthe Hyper Text Markup Language (HTML). In an HTML-encoded program,content is surrounded by codes that indicate the manner in which thebrowser presents the content to a user. Additionally, HTML encodescertain devices called “links” that allow a user to “navigate” the webby simply clicking on a sensitive area of the web page.

A document that contains “objects” or “components” like graphics, audioor video files, or charts in addition to text is called an embeddeddocument object. Several competing standards exist in the marketplacefor documents that can be transmitted over the Internet and displayed ina browser. For example, two such standards are OpenDoc, promoted by theInternational Business Machines Corporation and Object Linking andEmbedding (OLE), promoted by the Microsoft Corporation. Typically, thesestandards provide for an application programming interface (API) thatallows an independent software vendor (ISV) to develop applications thatdeliver components via the Internet. An API generally allows aprogrammer to interact with an enveloping browser. For example, aprogrammer may seek to determine the precise configuration of thebrowser by reading the values of its internal parameters. Alternatively,a programmer may wish to adapt the browser to a desired configuration byappropriately setting the browser's parameters.

Finally, a script is a list of computer-executable instructions,typically written in a human-readable language. Some browsers areconfigured to execute instructions written in script languages. In suchbrowsers, an analog of a Central Processor Unit (CPU)which is anessential component of all modern computers-is defined within thesoftware contained in the browser. This software-defined CPU executesthe scripts within the browser environment. For example, JavaScript™ isa language in which a programmer can code in a human-readable set ofinstructions that can be executed within the browser environment. Inthis case, the browser is said to be a “container” object to execute thescript within its bounds.

Referring now to the parent application, to achieve the objective statedtherein, a web browser program running on a client computer must be ableto access the inner workings of the client computer. This can beachieved with the help of the OLE document object technology. The OLEtechnology is a “system-level object architecture that includes servicesfor all-inclusive data access, remote distribution of softwarecomponents across heterogeneous platforms, robust transactionprocessing, and large group development.” & “OLE is?”, undated, (visitedDec. 12, 1998), <www.microsoft.com/oledev/olemkt/oleent/oleent.btm>.Active X™ technology, developed by the Microsoft Corporation, ofRedmond, Wash., uses the OLE architecture and provides the buildingblocks that enable a provider to distribute over a network softwareexecutables that can be executed on a client machine. In general, suchdistribution of software executables is done via a web browser asdescribed in the parent application. Typically, this execution on aclient machine is done when a page source is input to it by invokingcertain scripts embedded in the web browser. The downloaded softwarecomponents are called ActiveX™ controls, which are computer executablepieces of program code. One feature of ActiveX™ controls is hat theyhave no restrictions placed on them once they reach a user's machine.For example, a programmer may write an ActiveX™ control tat, upondownloading to a user's computer, can shut down the computer or reformatits hard drive thereby destroying all data stored on the computer. Thiscreates an easy way for malicious programs such as viruses to reach theclient computer and be executed without the user's notice.

To overcome these security problems, the Microsoft Corporation requiresall ActiveX™ controls to be verified by a signature initiative calledAuthenticode. This verification works in the following way. EachActiveX™ control is given a secure and encrypted digital signature by atrusted corporation. All browsers that allow download and execution ofActiveX controls are pre-programmed to verify the digital signature.Every time an ActiveX™ control is about to be downloaded, the browserexamines the digital signature associated with the control. If thesignature is verified as authentic by the browser, it is downloadedwithout any problems. Otherwise, the browser issues a warning message tothe user.

As explained in the parent application, the invention described thereinuses some of the features of a programming methodology exemplified byActiveX™ to effect easy and “hands-free” automatic downloading ofsoftware executables to a user's computer without any action taken onthe part of the user. While the invented method and system help achievethe stated ends, a security threat may be created because of theabove-mentioned feature of the ActiveX-like technologies that allowsunrestricted access by the embedded code to a user's computer.

Because computers today are interconnected by networks such as theInternet, computer security has become a more important issue thanbefore. Today, computers are more prone to attacks by viruses and TrojanHorses. A virus is a piece of computer code that replicates itselfwithout a user's intervention. Left unchecked, a virus may copy itselfstealthily to other computers and corrupt the data stored in storagedevices connected to the computers. For example, a virus may rewrite asection of a computer start-up program called the “boot sector”. Everytime a computer is started, the virus copies itself into the memory ofthe computer and waits. Suppose a user wishes to copy some data from thecomputer to a portable medium such as a floppy disk. The virus that hascopied itself to the memory could be programmed to intercept the writingof the data to the disk and copy itself to the disk along with the data.In this manner, the virus has replicated itself to the floppy disk andis now ready to infect other computers where the floppy disk is used.

In contrast to a computer virus, a “Trojan Horse” is a maliciouscomputer program that—like the fabled instrument of war used by ancientGreeks to gain entry into Troy—causes a user to believe that it is alegitimate program and entices the user operating a computer to performcertain actions that lead to compromising the security of the datastored in the computer.

Referring back to the parent application, assume that in accordance withthe invention described therein, an Internet Clinical Services Provider(ICSP) downloads a software program called QuickClean™, designed to“cleanup” the user's hard drive. In accordance with the above-mentionedActiveX™ Authenticode initiative, a license file is delivered to theuser along with the QuickClean program. This software is designed withembedded methods or sub-routines that, when invoked properly using ascript, rid the user computer of unwanted or unused software in anorderly manner. However, since these methods or sub-routines forremoving unwanted or unused software are invoked by a script, amalicious user can also invoke the script in such a way as to removedesirable or valuable software, thereby causing severe damage to theuser's computer. Moreover, a malicious user may also attempt to secretlytransfer the contents of a user's computer by e-mailing these to his owncomputer. In the computer security lingo, such a malicious user orprogrammer is called a computer “hacker.” The above-mentioned maliciousact, called computer “hacking,” can be accomplished in two ways.

In accordance with a first way of hacking, a hacker obtains a legitimatecopy of QuickClean™ and its associated license file from the ICSP. Thehacker can then create his own web site and host both QuickClean™ andthe associated Authenticode license file on his web site and inviteothers to use the “free” software. The hacker creates a web page on hisweb site that contains a malicious script that will use the methods orsub-routines in the QuickClean™ program to erase a user's hard disk.When a user, enticed by the “free” software downloads the web page fromthe hacker's web site, the hacker will download the QuickClean™ programto the user's computer and invoke the methods in the program to erasethe user's hard disk. Alternatively, suppose a user visits an authorizedICSP web site first and downloads the QuickClean™ program along with theassociated Authenticode license file. Later, the user visits thehacker's web site. Since the QuickClean™ program is already stored onthe user's computer, the hacker does not need to obtain a legitimatecopy to wreak havoc on a user's computer by providing a script to invokethe sub-routines embedded in the QuickClean™ program.

In accordance with a second way of hacking, a hacker may entice anunsuspecting user to visit his web site. The hacker may program his webpages to invoke multiple frames or multiple browser windows. In oneframe or browser window, the hacker can cause the user computer todownload the QuickClean™ program and the associated license file fromthe ICSP web site. In a second frame or browser window, the hacker canrun his malicious script, thereby causing damage as described above.

There is a need, therefore, for a system and method to prevent a hackerfrom activating the methods or sub-routines embedded in a computerexecutable code downloaded to a user computer via the web.

SUMMARY OF THE INVENTION

The present invention is a method to verify a downloaded software objectso that the software object is executed only if it is downloaded by anauthorized entity. Accordingly, the invention comprises a softwareprogram that is downloaded to a client computer by a server computer andis programmed to execute on the client computer only if it is enabled todo so. In a preferred embodiment of the invention, a computer-executableprogram code first determines the URL to which a browser running on theclient computer is pointed and enables the downloaded software programonly if the URL to which the browser is pointed is an authorized URL.

In another aspect of the invention, the determination of the URL towhich the browser is pointed is made by verifying the URL pertaining tothe “top-level” window of the browser. In a yet another aspect, thedetermination is made by verifying the URL pertaining to the “opener”window of the browser.

DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the invention willbe more readily apparent from the following detailed description of apreferred embodiment in which:

FIG. 1 shows a server computer connected to a client computer via theInternet; and

FIGS. 2A & 2B is a flow diagram depicting the steps comprising apreferred method to practice the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a client computer 100 is connected to the Internet102. Also connected to the Internet 102 is a server computer 104. Theclient computer 100 can be a personal computer (PC), and is equippedwith a processor, such as a Pentium II™ microprocessor, a display devicesuch as a computer monitor or a flat panel display, a memory such as asemiconductor memory, an input device such as a computer keyboard or amouse, and a storage device such as a computer hard drive. The clientcomputer 100 is configured to run an ActiveX™-compatible browser such asthe Microsoft® Internet Explorer browser program. The browser program isadapted to incorporate an embedded object model, facilitating thedelivery of objects by the server computer 104 to the client computer100. Though in the preferred embodiment a Microsoft® Internet Explorerbrowser and the ActiveX™ technology are discussed, these should not beviewed as limitations to the invention. While in the illustrativediscussion herein the technologies are enumerated as the best ways topractice the invention, the invention is contemplated to extend beyondthese specific modes of implementation.

As described in the parent application, the server computer 104 isoperated by an Internet Clinical Services Provider (ICSP). The servercomputer 104 comprises a processor, such as a Pentium II™microprocessor, a memory such as a semiconductor memory, and a storagedevice such as a computer hard drive. The server computer 104 isconfigured to receive request messages from the client computer 100 overthe internet in the Hyper Text Transfer Protocol (HTTP), File TransferProtocol (FTP) or any similar protocol used to transfer data, video,voice or a combination of these media. The server computer 104 isconfigured to transmit in response messages that include “web pages”that are programmed in Hyper Text Markup Language (HTML) or a similarlanguage. Embedded in the web pages are components such as documents,scripts, objects, frames and others that enable the server computer 104to display colorful graphical images on the display device coupled tothe client computer 100.

Now referring to FIGS. 2A and 2B, in accordance with the inventiondescribed in the parent application, a user operating the clientcomputer 100 enters the Universal Resource Locator (URL) pertaining tothe server computer 104 in a window provided by the browser programrunning on the client computer 100. When the user presses a “send”button on the browser, this causes a request message to be transmittedto the server computer 104. (Step 200). The server computer 104 thencauses an identification web page to be displayed on the browser windowat the client computer 100. After the user enters the appropriateidentification information in the browser window, this information istransmitted to the server computer. (Step 202).

The server computer 104 authenticates the user (Step 204), and ifauthenticated, proceeds to download a copy of an ActiveX™-control-likesoftware program and an associated license file to the client computer100. (Step 205). For the purposes of illustration, assume that thesoftware program is QuickClean™ and the license file is namedQuickCleanLicense. The license file works in conjunction with thesoftware program in the following way. When software objects embedded inthe software program are to be executed, the browser or another programrunning on the client computer 100 verifies if the license file and thesoftware objects are “related.” If they are found to be related, themethods (or sub-routines) within the software objects can be “invoked”by a script running on the client computer 100. (Step 206). If, on theother hand, QuickCleanLicense is found to be not related to QuickCleansoftware, then the client computer 100 terminates the program afterdisplaying or sounding an alarm message. (Step 220). It should be notedthat authentication of the user by the server computer 104 (described instep 204) and the verification of the software objects by the clientcomputer 100 (described in step 206) are different tasks and should notbe confused with each other.

The invented method adds an additional step to the art described in theparent application. After the client computer 100 determines that theQuickClean™ software and the QuickCleanLicense are “related,” the codein the QuickClean™ software must be “enabled” before it can be put tointended use. This is done by appropriately programming the QuickClean™software to perform a “first-check” and a “second-check” as follows.

In order to prevent the first method of hacking described in thisapplication, the QuickClean™ software is programmed to perform a“first-check” whereby it is determined if the browser is pointed to anICSP-authorized web site when the software is invoked by the scriptrunning on the client computer. When the script invokes a sub-routine ora method in the QuickClean™ software, a first set of instructionsembedded in the QuickClean™ software queries the browser to determinethe URL to which the browser is pointed. (Step 208).

A hacker may mislead the client computer 100 when it performs theabove-mentioned “first-check.” He can do this by causing the clientcomputer to open a new browser window or a new browser window frame,according to the second method of hacking described above. To preventthis, the following method is used to perform a “second-check” of theQuickClean™ software. This is accomplished by a second set ofinstructions embedded in the QuickClean software. The second set ofinstructions queries the browser to determine the URL pointed to by the“top-level” window and the “opener” window. (Step 210).

For example, if ActiveX™ objects embedded in an OLE-compatible browserare used to implement the QuickClean™ program, the URL to which thebrowser is pointed can be obtained by calling the method GetDisplayNameprovided in the Monicker Interface or by calling the GetLocation methodprovided in the Service Provider Interface of the IOleClientSite objectdefined within the ActiveX™ object. If both the methods (or subroutinecalls) return the same result, which is a ICSP-authorized URL, then theQuickClean™ software is deemed to have passed the “first check.” (Step208). These two methods can be illustrated as follows:

(1) IOleClientSite→MonickerInterface→GetDisplayName()

(2)IOleClientSite→ServiceProviderInterface→BrowserAppInterface→GetLocation()

Additionally, the ActiveX objects embedded in the OLE-compatible browsercan determine the URL pointed to by the “top-level” window of thebrowser by calling the BrowserApp Interface which can query the DocumentObject to obtain the HREF property of the Top Window Object. The“opener” window is determined in a similar manner. This can beillustrated in the following sequence of function calls:

(1)BrowserAppInterface→DocumentObject→WindowObject→TopWindowObject→LocationInterface→HrefProperty()=top-level URL

(2)BrowserAppInterface→DocumentObject→WindowObject→TopWindowObject→OpenerWindowObject→LocationInterface→HrefProperty=opener URL

Once it is determined that the “top-level” URL and the “opener” URLpoint to the same authorized URL, then the QuickClean™ software isdeemed “secondarily enabled.” (Step 210).

Upon a successful enablement according to steps 208 and 210, theQuickClean™ software is executed by scripts running on the clientcomputer 100. (Step 212). If, on the other hand, the QuickClean™software is not enabled according to steps 208 or 210, then an attemptby a script to run the software results in error messages. (Step 220).

There is described in the foregoing a new and useful invention toprevent a hacker from causing a threat to the information contained in aclient computer by misusing authenticated objects designed to performsecure tasks. One skilled in the art may make several modifications toor departures from the preferred embodiments provided herein withoutdeparting from the spirit and scope of the invention, or without undueexperimentation. For example, the order in which steps 208 and 210 areexecuted may be interchanged; other browser programs can be used topractice the invention; and the technologies described herein to deliverand execute software via a computer network may be replaced with othersimilar technologies. All such departures and modifications are withinthe scope of this invention and should be construed accordingly.

What is claimed is:
 1. A method to secure software downloaded from aserver computer to a client computer over a computer network, the methodcomprising: receiving a Universal Resource Locator (URL) pertaining to aserver computer in a browser window provided by a browser programrunning on a client computer; initiating the downloading of a web pageon the browser window on the client computer based on the URL, whereinthe web page has associated therewith a control software program with acorresponding digital signature; verifying the control software programusing the digital signature; displaying a first message if the controlsoftware program fails the verification; querying the browser program todetermine the URL to which the browser program is pointed; determiningwhether the URL to which the browser program is pointed is authorized;executing the control software program if it is determined that the URLto which the browser program is pointed is authorized; and displaying asecond message if it is determined that the URL to which the browserprogram is pointed is not authorized.
 2. The method of claim 1 andfurther comprising authenticating a user via the browser program.
 3. Themethod of claim 1 and further comprising invoking at least two of aplurality of methods provided by the browser program to determine if itis pointed to an authorized web site; and comparing the results obtainedby the methods that are invoked.
 4. The method of claim 1 and furthercomprising invoking at least one method provided by the browser programto obtain information located in a top-level browser window.
 5. Themethod of claim 1 and further comprising invoking at least one methodprovided by the browser program to obtain information located in anopener browser window.
 6. Computer executable program code stored on acomputer readable medium to implement the method of claim
 1. 7. A methodto secure software downloaded from a server computer to a clientcomputer over a computer network, the method comprising: receiving aUniversal Resource Locator (URL) pertaining to a server computer in abrowser window provided by a browser program running on a clientcomputer; initiating the downloading of a web page on the browser windowon the client computer based on the URL, wherein the web page hasassociated therewith a control software program with a correspondingdigital signature, wherein the control software program includescomputer maintenance software; verifying the control software programusing the digital signature; displaying a first message if the controlsoftware program fails the verification; querying the browser program todetermine the URL to which the browser program is pointed; determiningwhether the URL to which the browser program is pointed is authorized;executing the control software program if it is determined that the URLto which the browser program is pointed is authorized; and displaying asecond message if it is determined that the URL to which the browserprogram is pointed is not authorized.
 8. A method to secure softwaredownloaded from a server computer to a client computer over a computernetwork, the method comprising: receiving a Universal Resource Locator(URL) pertaining to a server computer in a browser window provided by abrowser program on a client computer; initiating the downloading of aweb page on the browser window on the client computer based on the URL,wherein the web page has associated therewith a control software programwith a corresponding digital signature; verifying the control softwareprogram using the digital signature; displaying a first message if thecontrol software program fails the verification; querying the browserprogram to determine the URL to which the browser program is pointed;determining whether the URL to which the browser program is pointed isauthorized; executing the control software program if it is determinedthat the URL to which the browser program is pointed is authorized;displaying a second message if it is determined that the URL to whichthe browser program is pointed is not authorized; determining a firstURL pointed to by a top-level window; determining a second URL pointedto by an opener window; and executing the control software program onlyif both the first URL and the second URL are authorized.